The panorama was collected by James B. Irwin at Station 2. David Scott is to the left of the rover. He is examining a boulder. The large hill to the left of the rover is the summit of Mt. Hadley Delta. (QuickTime, 400KB, note: this may take some time to download depending on your connection speed)

By using symbols, elements can be represented much more conveniently and much more briefly. This method of using symbols can be extended to compounds. You will now look further into this idea using a very familiar compound: water. Recall which atoms there are in a water molecule.

Question 24

Before going on to see how atoms can link (bond) with each other, you need to look at atoms in a little more detail. Doubtless they are not like blocks of Lego! So what are they like?

In fact, every atom has a complex internal structure. Given the extremely small size of an atom, you may find it difficult to visualise any smaller bits inside it. However, you may already be familiar with some of the effects of one of these components - electrons. It is easy to do an experiment tha

In these sections we have described some of the quantitative relationships between the physical dimensions of simple sounds and their subjective psychological dimensions. The physical dimension of intensity, or pressure amplitude, given in decibels (dB), directly affects loudness. Frequency of pressure changes, in hertz (Hz), mainly determines pitch.

The lowest threshold value and hence the maximal sensitivity for humans is in the region of 3000 Hz.

In preceding sections we examined two ways in which the auditory system may code frequency information: the place theory and phase locking. In this section we will look at the psychophysical evidence for place coding on the basilar membrane by examining the ability of the auditory system to resolve the components of sinusoidal waves in a complex sound – a phenomenon known as frequency selectivity.

The perception of a sound depends not only on its own frequency and intensity but also o

Psychophysics is the oldest field of the science of psychology. It stems from attempts in the nineteenth century to measure and quantify sensation. It attempts to quantify the relationship between a stimulus and the sensation it evokes, usually for the purpose of understanding the process of perception. Historically, psychophysics has centred around three general approaches. The first involves measuring the smallest value of some stimulus that a listener can detect – a measure of sensitivit

We have seen that in the cochlear nerve, information about sound intensity is coded for in two ways: the firing rates of neurons and the number of neurons active. These two mechanisms of coding signal intensity are found throughout the auditory pathway and are believed to be the neural correlates of perceived loudness. The tonotopic organisation of the auditory nerve is also preserved throughout the auditory pathway; there are tonotopic maps within each of the auditory nerve relay nuclei, the

The tectorial membrane runs parallel to the basilar membrane, so when the basilar membrane vibrates up and down in response to motion at the stapes, so does the tectorial membrane. However, as shown in Figure 14, the displacement of the membranes causes them to pivot about different hinging points and this creates a shearing force betw

The inner ear (Figure 3) can be divided into three parts: the semicircular canals, the vestibule and the cochlea, all of which are located in the temporal bone. The semicircular canals and the vestibule affect the sense of balance and are not concerned with hearing. However, the cochlea, and what goes on inside it, provides

Figure 1 is a diagram of the human ear. The outer ear consists of the visible part of the ear or pinna, the external auditory canal (meatus), and the tympanic membrane (tympanum) or eardrum. The human pinna is formed primarily of cartilage and is attached to the head by muscles and ligaments. The deep central portion of the

Despite the impact of relativity, the greatest source of change in the scientific world-view in the twentieth century has undoubtedly been the development of quantum physics. This is the branch of physics that is mainly concerned with microscopic entities such as atoms and molecules, and their constituents. It is by far the most quantitatively accurate part of science, routinely providing predictions that are correct to just a few parts in a million. Quantum physics is also of enormous

The first half of the nineteenth century was a period of great economic and industrial growth. The steam engine, invented in the previous century, was becoming increasingly common in locomotives, mines and factories; power was becoming available on demand. A major priority for engineers was to produce more efficient engines, in order to deliver more useful power for less expenditure on fuel. Thermodynamics emerged as a study of the basic principles determining energy flows and the effi

The first genetically modified organisms (GMOs) were created in the early 1970s, but for much of the 1980s biotechnology was a phenomenon confined to the laboratory. In 1988, 'vegetarian cheese', the first food product created using GMOs, was introduced in the UK. This cheese was produced using chymosin, an enzyme derived from genetically modified bacteria, rather than the traditional animal product (rennet). Chymosin derived from GMOs is now used to produce 90% of the hard cheeses mad

In the early 1990s, biotechnology companies were preparing to market the first food products derived from GM crops. This provided a challenge to legislators. There were no precedents to guide them as to how to approve or ban novel food products. The methods used to approve pharmaceuticals, summarised above (Section 3.1), did not seem to transfer easily to whole food products.

Pusztai and his team were attempting to develop suitable tests to assess the safety of GM potatoes. Typically, testing the safety of GM food involves comparing its composition and/or its effects with that of the conventionally produced food it most closely resembles. We have seen that such comparisons were at the heart of Pusztai's work.

The comparison of GM and conventional crops and food has led to the so-called principle of substantial equivalence, which has been used extensiv